Project 1. Targeted Radiotherapy of Neoplastic Meningitis using Monoclonal Antibodies Labeled with Alpha Particle Emitting [211] At. Michael Zaiutsky, Ph.D., Project Leader Neoplastic meningitis (NM), characterized by the dissemination of malignant tumor cells within the leptomeningeal space and metastatic spread along the brain and spine, is a devestating disease resulting in a median survival of only 2-6 months. In terms of number of patients affected, breast and lung carcinoma are the most common primary sites that metastasize to the leptomeninges. We propose to focus initially on the rapid translational development of a targeted radiotherapeutic for breast carcinoma NM and if successful, apply the same approach to lung carcinoma. Our strategy is to combine trastuzumab with the a-particle emitter ^^^At because these a-particles have a greater cytotoxic effectiveness than conventional radiation and have a range in tissue of only a few cell diameters, characteristics that offer important advantages for NM treatment. We seek to determine the best method for labeling trastuzumab not only for[211]At but also for [124] l to move fonward to clinical investigation. If we can establish similar in vivo behavior for mAb labeled via the two radiohalogens, PET imaging with [124] l-labeled trastuzumab could provide a valuable tool for determining radiation dosimetry, evaluating distribution within the neuroaxis, and individualizing patient treatment protocols for [211]At-labeled trastuzumab. Our Specific Aims are: 1) To label trastuzumab with [211]At and [124] l using methodologies designed to minimize dehalogenation and maximize entrapment of radioactivity within tumor cells after labeled mAb internalization; 2) to evaluate these radiolabeled trastuzumab conjugates in human breast carcinoma cells in vitro, and tissue distribution in mice with subcutaneous breast carcinoma xenografts and in an athymic rat NM model of HER2 expressing breast carcinoma; 3) to determine the therapeutic efficacy, neuroaxis distribution, toxicity, and radiation dosimetry in athymic rat models of NM; 4) To obtain FDA Investigational New Drug permits for the best [211] At- and [124] l-labeled trastuzumab conjugates, and then to conduct clinical trials in patients with breast carcinoma NM and 5) Using the same translational paradigm determine the best strategy for labeling panitumumab with [211]At and [124] I and evaluate their potential as targeted radiotherapeutics and diagnostics for patients with lung carcinoma NM.